Industrial cart comprising a mother or primary cart and a secondary or daughter cart

ABSTRACT

An industrial cart system and method for operation thereof. The industrial cart system comprises a mother cart and a daughter cart. The mother cart comprises an upper frame and a lower frame. According to an embodiment, the lower frame is configured to support the daughter cart in a loaded or travel position. The lower frame is further configured to allow two-way loading and unloading of the daughter cart. According to another embodiment, the mother cart comprises a chassis and one or more lift mechanisms operatively coupled to the lower frame. The chassis is configured to support the daughter cart and the lift mechanisms are configured to lower and raise the chassis (and the daughter cart) to facilitate the loading and unloading of the daughter cart.

RELATED APPLICATIONS

The present application claims convention priority from U.S. ProvisionalPatent Application No. 62/003,995 filed on May 28, 2014, and theentirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to industrial cart systems, and moreparticularly, to industrial cart comprising a mother or primary cart anda secondary or daughter cart.

BACKGROUND OF THE INVENTION

In the art, forklifts have traditionally been used to deliver or movematerials, for example, palletized loads, in a factory or otherindustrial plant. For a variety of reasons, including safety concerns,plants have been moving to being “forklift free”.

The movement of materials or parts and/or material containers in a plantis typically done using automated guided vehicles (“AGV”) or aman-on-board system or a combination of both. In a typical man-on-boardsystem, the material or components are moved in plant using a train ofcarts, and a human operator unloads the carts and removes empty carts.Because a human operator is involved, there will be limits on the sizeand/or weight of loads and/or cart configurations that can be handled,for example, based on a safety and/or physical handling considerations.

Accordingly, there remains a need for improvements in the art.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed to an industrial cart systemcomprising a mother and daughter configuration. According to anexemplary implementation or application one or more mother/daughter cartunits are coupled together and moved through an industrial plant by atractor or other drive mechanism. The daughter cart is disengageablefrom the associated mother cart and is offloaded or disengaged, forexample, to deliver parts, components or other materials, at a workstation or assembly station in the plant. The empty daughter cart isloaded back onto the mother cart and moved.

According to another exemplary implementation or embodiment, a method orprocess is provided comprising coupling one or more mother/daughter cartunits together and moving the coupled mother/daughter cart units throughan industrial plant utilizing a tractor, or a drive mechanism integratedwith the industrial plant, for delivery of parts, components or othermaterials, or removal or transfer of parts, components or othermaterials, at or from one or more work stations or assembly stations inthe industrial plant.

According to one aspect, the present invention comprises a mother cartsuitable for transporting a daughter cart, the mother cart comprises: alower frame; an upper frame, the upper frame being connected to thelower frame; the lower frame including a plurality of wheels configuredto allow the mother cart to be moved; the lower frame including aplurality of support guides, the support guides being configured tosupport the daughter cart in a raised position to provide apredetermined ground clearance; and the lower frame having two opensides so as to provide for two-way loading and unloading of the daughtercart on the mother cart.

According to another aspect, the present invention comprises mother cartsuitable for transporting a daughter cart, the mother cart comprises: alower frame; an upper frame, the upper frame being connected to thelower frame, and the lower frame providing a support structure; thelower frame including a plurality of wheels configured to allow themother cart to be moved; a chassis, the chassis spanning the lower frameand being configured to provide a predetermined ground clearance, thechassis including first and second daughter cart channels, wherein eachof the daughter cart channels is configured to support a section of thedaughter cart.

According to yet another aspect, the present invention comprises anindustrial cart train comprising: two or more mother carts coupledtogether to form a parts delivery system suitable for an industrialapplication; each of the mother carts comprising, a lower frame; anupper frame, the upper frame being connected to the lower frame; thelower frame including a plurality of wheels configured to allow themother cart to be moved; the lower frame including a plurality ofsupport guides, the support guides being configured to support adaughter cart in a raised position to provide a predetermined groundclearance; and the lower frame having two open sides so as to providefor two-way loading and unloading of the daughter cart on the mothercart.

According to a further aspect, the present invention comprises anindustrial parts delivery system comprising: two or more mother cartscoupled together to form a train of carts, and one of the mother cartsbeing configured to be coupled to a tractor; the mother cart comprising:a lower frame; an upper frame, the upper frame being connected to thelower frame, and the lower frame providing a support structure; thelower frame including a plurality of wheels configured to allow themother cart to be moved; and a chassis, the chassis spanning the lowerframe and being configured to provide a predetermined ground clearance,the chassis including first and second daughter cart channels, whereineach of the daughter cart channels is configured to support a section ofa daughter cart.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of embodiments of the invention and/or the accompanyingfigures.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to the accompanying drawings which show, byway of example, embodiments of the present invention, and in which:

FIG. 1A shows in diagrammatic form a mother or primary cart with adaughter or secondary cart in the engaged or loaded position orconfiguration according to an embodiment of the present invention;

FIG. 1B shows the mother cart of FIG. 1A with the daughter cart removed;

FIG. 1C shows a side view of the mother cart of FIG. 1A with a daughtertilt cart in the mounted or loaded position;

FIG. 1D is a partial view of the lower frame of the mother cart of FIG.1A and showing the daughter cart support members/loading guides in moredetail;

FIG. 2A shows the mother cart of FIG. 1B with the daughter cart removedor disengaged from the mother cart, and with a locking bar in a down orlocked position;

FIG. 2B shows a close up view of the locking end of the locking bar ofFIG. 2A according to an embodiment of the invention;

FIG. 2C shows a close up view of the hinged or pivot end of the lockingbar of FIG. 2A according to an embodiment of the invention;

FIG. 3A shows a mother cart with a lower chassis according to anotherembodiment of the present invention;

FIG. 3B shows the mother cart of FIG. 3A configured with vertical liftmechanisms or actuators according to another embodiment of the presentinvention;

FIGS. 4A and 4B show views of the mother cart of FIG. 3B in the raised,e.g. loaded or travel position;

FIGS. 5A to 5C show views of the mother cart of FIG. 3B in the loweredor daughter cart unloading/loading position;

FIG. 6 is a reproduced photograph of an exemplary industrial plant orfacility configured with a “CC-5” chain mechanism configured for movinga train of one or more mother/daughter carts according to the presentinvention

FIG. 7A shows a flat top daughter cart according to an exemplaryimplementation or embodiment of the invention;

FIG. 7B shows a flat top daughter cart according to another exemplaryimplementation or embodiment of the invention;

FIG. 8 shows the flat top daughter cart of FIG. 7A in more detail;

FIG. 9 shows a “plastic pallet” daughter cart according to an exemplaryimplementation or embodiment of the invention;

FIG. 10A shows a “tilt-top” daughter cart according to an exemplaryimplementation or embodiment of the invention;

FIG. 10B shows the tilt-top daughter cart of FIG. 9A loaded with a binor crate;

FIG. 10C shows the tilt-top daughter cart of FIG. 9C with the tiltplatform in a tilted position;

FIG. 11 shows a plurality of mother/daughter carts according to anembodiment of the invention coupled together to form an industrial partsor components delivery system or train;

FIG. 12A shows a plurality of mother/daughter carts according to anotherembodiment of the invention coupled together to form an industrial partsor components delivery system or train; and

FIG. 12B is a top view of the industrial parts delivery system or trainof FIG. 12B.

In the drawings, like reference numerals indicated like components orelements.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

Reference is first made to FIGS. 1A and 1B, which show a mother cart anda daughter cart configuration according to an embodiment of the presentinvention and indicated generally by reference 10. The mother or primarycart indicated generally by reference 100 is configured to carry ortransport a daughter or secondary cart indicated generally by reference200. The daughter cart 200 may take various forms, some of which aredescribed in more detail below, and is generally configured to carry aload, for example, automotive components or parts in a bin or othercontainer, as indicated by reference 210 in FIG. 1A, that is loaded ontothe daughter cart or an integral component of the daughter cart 200. Aswill be described in more detail below, the mother cart 100 isconfigured to provide for two-way loading and unloading of the daughtercart 200. The daughter cart 200 may be implemented in a number ofconfigurations as will be described in more detail below. The mothercarts 100 are configured to be coupled together to form a series, e.g. atrain, of mother/daughter carts 10, which can be moved through anindustrial facility or plant, for example, by a tractor, or other humanoperated or automated machine, pulling the mother carts 100, or, forexample, by a moving or motive mechanism installed in the industrialfacility, such as a CC-5 chain mechanism (as shown in FIG. 6).

Reference is next made to FIG. 1B, which shows the mother cart 100 ofFIG. 1A with the daughter cart 200 removed, i.e. unloaded. As shown, themother cart 100 comprises a lower frame indicated generally by reference110 and an upper frame indicated by reference 120. The lower frame 110includes wheels or castors 112, indicated individually by references 112a, 112 b, 112 c and 112 d. As shown, the mother cart 100 includes a towbar 116 and a hitch 118. The tow bar 116 is configured to couple orengage the hitch 118 of another mother cart 100 or a tractor for movingor pulling the mother cart(s) 100 through an industrial plant orfacility. According to an exemplary implementation or embodiment, themother cart 100 may include daughter cart removal assist handles 122, asshown in FIGS. 1B and 2A, and indicated individually by references 122a, 122 b, 122 c and 122 d. The daughter cart assist handles 122 areconfigured to provide a mechanical advantage to assist an operator withthe removal of a daughter cart from the mother cart 100 (and function inconjunction with the daughter cart support members or loading guides asdescribed below). According to an embodiment, the mother cart 100, i.e.the lower frame 110 and the upper frame 120, are configured to providetwo-way loading and unloading of the daughter cart 200, i.e. from eitherside of the mother cart 100.

As shown in FIGS. 1B and 2A, the lower frame 110 comprises a row orseries of daughter cart support members or loading guides 111, each ofthe rows is indicated by references 113 a and 113 b. The daughter cartsupport members 111 are configured to support respective sides of thedaughter cart 200 in the loaded position on the mother cart 100.According to an exemplary embodiment, the daughter cart support members111 are implemented using a plurality of appropriately sized boltssecured into respective positions in the interior side wall of the lowerframe 110 of the mother cart 100. Each of the daughter cart supportmembers 111 comprises a bearing to facilitate movement of the daughtercart 200 for loading and unloading from the mother cart 100. Accordingto another aspect or exemplary implementation the loading guides 111include Delrin™ polymer applied to contact surfaces to reduce friction.According to an embodiment, the daughter cart support members or loadingguides 111 comprise a curve-linear or sloped configuration, for example,a 15 degree tapered lead-in, as depicted in FIG. 1D, to facilitate theloading and unloading of the daughter cart 200 from the mother cart 100.According to another embodiment, one of the loading guides, indicated byreference 111′ in FIG. 1D, is configured to function as roll-offretarder for the daughter cart 200. According to an exemplaryimplementation, the loading guide 111′ is configured as a fixed guide,e.g. does not include a bearing or other rolling surface in order toprovide resistance, or a stop, to the egress of the daughter cart 200from the mother cart 100.

According to an exemplary implementation or application, the mother cart100 shown in FIGS. 1A and 1B is configured carry standard 48″×48″ palletboxes, pallet/tray packs, and/or pallet/tote packs, as will be readilyfamiliar to those skilled in the art. According to another aspect, themother cart 100 is configured to provide a ground or floor clearance ofapproximately 1½″ for the daughter cart 200 (e.g. the castors of thedaughter cart 200) as shown in FIG. 1C. According to another aspect orexemplary implementation, the mother cart 100 is configured to provide aground or floor clearance of approximately 2½″ for a CC-5 chain in floorapplication. The CC-5 chain in floor mechanism is an industry standardwithin the understanding of those skilled in the art. If the CC-5 chainconfiguration is higher than 2″, then the mother cart 100 is configuredwith a greater clearance, as will be readily apparent to one skilled inthe art. According to another aspect, the arrangement of the lower frame110 and the upper frame 120 of the mother cart 100 are configured toprovide an optimized center of mass (e.g. a lower center of mass) of thedaughter cart and load. According to an exemplary implementation, thelocation of the castors (wheels) is configured to optimize stability ofthe mother cart when carrying a daughter and associated load, for a50×50 tilt top daughter, for example, as depicted in FIG. 1C.

As shown in FIG. 2A, the mother cart 100 is configured with a lockingbar on each side of the cart indicated by references 124 a and 124 b(for a two-way loading configuration). As shown in FIGS. 2A and 2B, oneend of the locking bar 124 is attached or coupled to the lower frame 110of the mother cart 100 by a hinge or pivot mechanism 128, indicatedindividually by references 128 a and 128 b, and configured to allow thelocking bar 124 to move between an open position indicated by reference130 and a closed or locked position indicated by reference 132 in FIG.2A. The other end of the locking bar 124 is engaged or locked in theclosed position 132 by a lock mechanism or clasp 126, indicatedindividually by references 126 a and 126 b in FIG. 2C.

According to another embodiment or exemplary implementation, one of thelocking bars 124 is permanently connected in the closed position 132 toincrease the structural integrity of the lower frame 110, and/or providea configuration where one-sided loading/unloading is preferred for theparticular industrial application or physical plant configuration.

Reference is next made to FIG. 3A, which shows a mother cart accordingto another embodiment of the present invention and indicated generallyby reference 101. In addition to the components and elements describedabove, the mother cart 101 includes a chassis indicated generally byreference 121 in the lower frame 110 as shown. The chassis 121 isconfigured to provide increased structural integrity or strength for themother cart 101 and comprises a pair of daughter cart tracks or channels320, indicated individually by reference 320 a in FIG. 3A and reference320 b in FIG. 3B. The daughter cart tracks 320 are configured to receiveand support the wheels or castors (or support base) of the daughter cart200 loaded onto the mother cart 100. In accordance with this embodimentor an exemplary implementation thereof, the daughter cart tracks 320provide a support surface for the daughter cart 200 and therebyeliminate the need for the daughter cart support and loading guides 111(as described above). The configuration of the chassis 121 and thedaughter cart tracks 320 also provides for the capability of two-wayunloading and loading of the daughter cart(s) for example as describedabove.

As shown in FIGS. 3A and 3B, the chassis 121 includes a belly plate 324,which may be configured as a support surface for the daughter cart 200.As shown in FIG. 3A, the lower frame 110 includes the loading guides 111and the roll-off retarder guide indicated by reference 111′, as wasdescribed in more detail above. According to an exemplaryimplementation, the lower frame 110 and the chassis 121 for the mothercart 101 are configured to provide a floor clearance of approximately1½″.

Referring back to FIG. 3B, one or both of the daughter cart tracks 320includes a locking slot indicated generally by reference 322. Thelocking slot 322 is configured to engage the lower frame of the daughtercart 200, for example, a movable or retractable locking member, andthereby secure the daughter cart 200 when the chassis 121 is raised tothe travel position. It will be appreciated that the locking slot 322can supplement the function of the locking bars 124 (as describedabove), and furthermore, in some applications or implementations, thelocking slot 322 may eliminate the need for the locking bars 124, aswill be readily understood by skilled in the art.

Referring still to FIG. 3B, according to an embodiment, the mother cart101 includes a lift mechanism operatively coupled to each of the castorsor wheels 112, and indicated individually by references 114 a, 114 b,114 c and 114 d. The lift mechanism 114 comprises an actuator, forinstance, a hydraulic actuator, and is configured to move the lowerframe 110 and the chassis 121 of the mother cart 101 between a raised orloaded position as shown in FIG. 4A, and indicated generally byreference 401, and a lowered or unloading position as shown in FIG. 5Band FIG. 5C and indicated generally by reference 501. According to anexemplary implementation, the lift mechanism 114 is responsive tocontrol signals generated by a controller installed in a control panelor unit, indicated generally by reference 340 in FIG. 3B, in response toan input or actuation by an operator, for raising and lowering thechassis 121 for loading and unloading the daughter cart 200. Forexample, the controller may be implemented as a hardware microprocessoror microcontroller configured to execute instructions and commandsprogrammed in computer software and stored as executable instructions inmemory operatively coupled to the hardware processor for execution inperforming the control functions and other associated operations. In anexemplary implementation, the control panel 340 includes controls 342,e.g. buttons, responsive operator actuation, and may further include adisplay module 344, and other control/status modules. As shown in FIG.4A, a castor support frame 410 (indicated individually by references 410c and 410 d in FIG. 4A) is provided for each of the castors 112. Thecaster support frame 410 is configured to operatively couple the castor112 to the lift mechanism 114. According to an exemplary implementation,the lift mechanism or actuators 114 comprise a bidirectional DC motordriven pump with an integral hydraulic cylinder such as the Parker™Compact EHA unit available from the Parker Hannifin Corporation. Theparticular implementation details for the lift mechanism and castorconfiguration, for example, setup, controller hardware and software orfirmware configuration and power, will be readily within theunderstanding of one skilled in the art.

It will be appreciated that the configuration of the mother cart 101with the lift mechanism provides the capability to adjust or vary thefloor or ground clearance, for example, using set point controls orsetting for the motors 114. This functionality allows the mother anddaughter cart system 10 to be configured for different applications orindustrial plant or facilities, for example, CC-5 chain installationwith greater than 2″ clearance. The mother cart 101 with the liftmechanism also provides the capability to improve the ergonomics andhandling of loading and unloading daughter carts by allowing the chassis121 to be lowered almost flush with the factory floor.

According to an exemplary implementation, the mother cart 101 shown inFIG. 3B is configured to provide a ground clearance of approximately 1½″in the raised or loaded position, as indicated generally by reference403 in FIG. 4B. In the lowered or unloading position 501, the lowerframe or chassis 110 is substantially flush with the ground or floor,for example, as depicted in FIG. 5C. It will be appreciated that theability to lower the chassis 121 and provide a reduced or substantiallyflush ground clearance facilitates moving a daughter cart 200 on (i.e.loading) and off (i.e. unloading) from the mother cart 101. To furtherfacilitate moving the daughter cart 200 on and off the mother cart 101,the daughter cart tracks 320 may include a ramp or beveled edge section,indicated generally by reference 420 in FIGS. 4A, 4B and 5B, 5C.According to another exemplary implementation or application, the lowerframe 110 and the chassis 121 are configured with the lift mechanism toprovide ground clearance between the mother cart and the loadeddaughter, e.g. 2.5 to 3″, as depicted in FIG. 7. This allows a traincomprising one or more mother carts (and associated daughter carts) tobe moved in the plant while providing increased clearance, for example,for CC-5 chains configured higher than 2″.

Referring to FIGS. 4A and 4B, the mother cart 101 may include a guideindicated generally by reference 430. The guide 430 is configured on theinterior surface of the lower frame 110 and adjacent the daughter carttrack 320. The guide 430 is configured to facilitate the positioning andthe movement of the daughter cart 200 in and out of the track 320.

In operation, the chassis 121 is lowered to rest on the factory floor orin close proximity to the factory floor in the lowered or unloadingposition 501. This allows the daughter cart 200 to be unloaded and/orloaded manually (i.e. by a human operator), or by an automated actuator(e.g. an industrial robot). It will be appreciated that because thedaughter cart 200 does not have to move up or down any appreciable slopeor incline to be loaded (or unloaded) on the mother cart 101, thedaughter cart 200 is more manageable by a human operator and may alsocarry heavy loads, i.e. payloads, and as a result be used in a widerrange of applications or part delivery/movement operations in a plant.As described above, beveled or sloped leading edge or ramp 420 on eachof the daughter cart tracks 320 allows the wheels of the daughter cart200 to more freely roll on or off the mother cart 101, furtherfacilitating moving or loading the daughter cart 200 onto and off of themother cart 101.

Reference is next made to FIGS. 7A and 7B, which show embodiments of aflat top daughter cart, indicated individually by references 710 and720. The flat top cart 710 comprises a “50×50” configuration as will beunderstood by one skilled in the art. The flat top cart 720 comprises a“34×50” configuration as will also be understood by one skilled in theart.

Reference is next made to FIG. 8, which shows the flat top cart 710 inmore detail. As shown, the flat top cart 710 comprises a frame 711 andcastors 712, indicated individually by references 712 a, 712 b, 712 cand 712 d. The flat top cart 710 may also include Delrin™ strips toreduce friction on contact surfaces and thereby facilitate loading andunloading the cart 710 from the mother cart 100. Another variant of theflat top cart is a plastic pallet as shown in FIG. 9 and indicatedgenerally by reference 900. In known manner, the daughter carts areloaded with parts or components for transport in an industrial facility,for example, automotive transmissions. Also in known manner, thedaughter carts may be fitted with a bin or other type of container,which is then used to carry parts or components, for example, airfilters, in an automotive assembly plant or application.

Reference is next made to FIGS. 10A, 10B and 10C which show a daughtertilt cart, indicated generally by reference 1000. The daughter tilt cart1000 comprises a base 1010 configured with castors or wheels as shown.The daughter tilt cart 1000 comprises a tilt platform 1020 which isoperatively coupled to the base 1010 through a hinge or pivot mechanismindicated generally by reference 1030. The tilt platform 1020 isconfigured to support a load, e.g. a bin, as shown in FIG. 10B, andindicated generally by reference 1100. As shown in FIG. 10C, thedaughter tilt cart 1000 includes an actuator, for example, a hydrauliccylinder mechanism, that is operatively coupled to the base 1010 and thetilt platform 1020 and configured to move, i.e. pivot, the tilt platform1020 and the bin 1100 to a tilted position as indicated by arrow 1200.The particular implementation details of the daughter tilt cart 1000 arereadily within the understanding of one skilled in the art.

One or more mother carts are coupled together to form a train or partsdelivery system which is moved through an industrial plant or factory,e.g. an automotive assembly plant, by a tractor, engine other drive orpropulsion system (not shown). For example, as shown in FIG. 11, aplurality of the mother carts 100 (described above with reference toFIGS. 1A-1D and FIGS. 2A-2C), indicated individually by references 100a, 100 b, 100 c, . . . 100 n are coupled together through the tow-bar116 and hitch 118 to form an industrial parts delivery system and train,indicated generally by reference 1100. Similarly, a plurality of themother carts 101 (described above with reference to FIGS. 3A-3B, FIGS.4A-4B and FIGS. 5A-5C), indicated individually by references 101 a, 101b, 101 c, . . . 101 m are coupled together through the tow-bar 116 andhitch 118 to form an industrial parts delivery system and train,indicated generally by reference 1200, for example, as depicted in FIGS.12A and 12B.

The present invention may be embodied in other specific forms withoutdeparting from the spirit or essential characteristics thereof. Certainadaptations and modifications of the invention will be obvious to thoseskilled in the art. Therefore, the presently discussed embodiments areconsidered to be illustrative and not restrictive, the scope of theinvention being indicated by the appended claims rather than theforegoing description, and all changes which come within the meaning andrange of equivalency of the claims are therefore intended to be embracedtherein.

What is claimed is:
 1. An industrial parts delivery system comprising:two or more mother carts coupled together to form a train of carts, andone of said mother carts being configured to be coupled to a tractor;each of said mother carts comprising: a lower frame; an upper frame,said upper frame being connected to said lower frame, and said lowerframe providing a support structure; said lower frame including aplurality of wheels configured to allow the mother cart to be moved; achassis, said chassis spanning said lower frame and being configured toprovide a predetermined ground clearance, said chassis including firstand second daughter cart channels, wherein each of said daughter cartchannels is configured to support a section of a daughter cart; saidlower frame having two open sides so as to provide for two-way loadingand unloading of the daughter cart on said mother cart; and wherein eachof said mother carts includes a lifting mechanism comprising a hydraulicactuator configured to raise and lower said chassis between an unloadingposition and a loaded position, and in said unloading position saidpredetermined ground clearance being reduced to a minimum groundclearance so as to facilitate movement of the daughter cart on and offthe mother cart.
 2. The industrial parts delivery system as claimed inclaim 1, wherein each of said daughter cart channels further includes asloped edge configured to facilitate movement of the daughter cart ontothe daughter cart channels.
 3. A mother cart suitable for transporting adaughter cart, said mother cart comprising: a lower frame; an upperframe, said upper frame being connected to said lower frame, and saidlower frame providing a support structure; said lower frame including aplurality of wheels configured to allow the mother cart to be moved; achassis, said chassis spanning said lower frame and being configured toprovide a predetermined ground clearance, said chassis including firstand second daughter cart channels, wherein each of said daughter cartchannels is configured to support a section of the daughter cart; saidlower frame having two open sides so as to provide for two-way loadingand unloading of the daughter cart on said mother cart; a liftingmechanism and said lifting mechanism being configured to raise and lowersaid chassis between an unloading position and a loaded position, and insaid unloading position said predetermined ground clearance beingreduced to a minimum ground clearance so as to facilitate movement ofthe daughter cart on and off the mother cart, said lifting mechanismcomprising a motor unit operatively coupled to each of said wheels and acontroller, and said motor units being responsive to one or more controlsignals generated by said controller for lowering and for raising saidchassis; and wherein each of said daughter cart channels includes asloped edge configured to facilitate movement of the daughter cart ontothe daughter cart channels.